The invention relates to improvements in apparatus for and in methods of increasing the permeability of wrapping material for rod-shaped products, especially rod-shaped smokers' products, and more particularly to improvements in methods of and apparatus for perforating tubular envelopes or wrappers of cigarettes or the like.
It is well known to enhance: the permeability of cigarette paper or other wrapping material for rod-shaped tobacco fillers and/or rod-shaped filters for tobacco smoke prior as well as subsequent to the conversion of a running web of wrapping material into a tubular envelope forming part of a continuous tobacco-containing rod; the leader of such rod is thereupon severed at regular intervals to yield a succession of discrete cigarettes, cigars, cigarillos or other rod-shaped smokers' products. It is equally known to enhance the permeability of selected portions of tubular envelopes forming part of discrete plain or filter cigarettes or analogous rod-shaped smokers' products while the products rotate about their own axes.
As a rule, a modem apparatus for enhancing the permeability of selected portions of a running web or of selected portions of tubular wrappers of successive rod-shaped smokers' products (hereinafter called cigarettes for short) comprises at least one source of high-energy radiation (such as a laser beam) and means for directing the beam or beams into one or more selected portions of the path for a running web of wrapping material or of the path for successive plain or filter cigarettes. If the apparatus is designed to perforate the finished (tubular) wrappers of plain or filter cigarettes, the cigarettes are caused to roll about their own longitudinal axes while moving sideways past the perforating station. The purpose of the perforating treatment is to ensure that the permeability of the tubular wrappers rises to a value at which an optimum quantity of atmospheric air is caused to enter the column of tobacco smoke flowing from the lighted end of a cigarette toward the mouth of the smoker. Cool atmospheric air is believed to exert a beneficial influence upon the nicotine and/or condensate contents of tobacco smoke.
U.S. Pat. No. 5,148,818 discloses a perforating apparatus which employs a source of coherent radiation (hereinafter called laser). The means for rolling successive cigarettes about their respective axes during advancement past the perforating station employs two coaxial drum-shaped conveyors and an endless flexible band. The path for the cigarettes is flanked by the band on the one hand, and by the conveyors on the other hand. The speed of the belt departs from the peripheral speeds of the conveyors, and this causes the cigarettes to roll about their respective axes. The laser is installed midway between the two rotary conveyors, and the beam of coherent radiation issuing from the laser is caused to circulate while impinging upon a tubular wrapper at a selected frequency to thus provide the wrapper with an array of perforations.
Published German patent application Serial No. 33 10 930 discloses a perforating apparatus wherein the peripheral surface of a rotary drum-shaped conveyor transports a series of cigarettes sideways past a station where the wrappers of the cigarettes are acted upon by a laser beam. The laser is confined in and is caused to move relative to a complex heart-shaped reflector. Such apparatus are complex, bulky and unreliable.
Another perforating apparatus is disclosed in published German patent application Serial No. 34 31 051 which proposes a different combination of a mobile laser and a directing system for the laser beam. The directing system employs a complex array of mirrors and rotary reflectors which are intended to focus a laser beam upon successive cigarettes while the cigarettes rotate about their respective axes and are simultaneously advanced sideways by a rotary conveyor toward, past and beyond the perforating station.
Published German patent application Serial No. 34 31 067 discloses an apparatus which combines the features of the apparatus disclosed in the aforediscussed published German patent applications Serial Nos. 33 10 930 and 34 31 051.
Published German patent application Serial No. 42 18 266 discloses a perforating apparatus wherein the cigarettes are transported and rolled by a set of drum shaped conveyors one of the conveyors carries a polygonal mirror which serves to direct a laser beam into the path for the cigarettes.
A further perforating apparatus is disclosed in published German patent application Serial No. 27 51 522. This publication proposes to roll successive cigarettes between the peripheral surface of a rotary drum-shaped conveyor and the complementary concave surface of a stationary rolling member. A laser beam trails successive cigarettes during sidewise movement of the cigarettes in an arcuate rolling channel between the moving peripheral surface of the drum-shaped conveyor and the stationary surface of the rolling member. The movement of the laser beam is initiated and regulated by a rotary drum-shaped member having a mirrored peripheral surface.
A drawback which is common to all of the above-enumerated perforating (permeability enhancing) apparatus is that the space requirements of such apparatus are excessive, that the apparatus are complex and hence expensive, as well as that their perforating action cannot be regulated and maintained with a desired or required degree of accuracy and facility.
Another drawback of certain conventional perforating apparatus is that, owing to their kinematics, the tubular wrapper of a cigarette can be perforated only during one-half of each revolution of a cigarette about its axis. Therefore, such apparatus are set up to expose the cigarettes to the action of laser beams which penetrate through the entire cigarette so that each beam provides perforations which are angularly offset by 180 degrees. Such solution is not entirely satisfactory because the energy requirements of the laser are very pronounced and also because the dimensions of at least one of two simultaneously burned perforations in the tubular wrapper of the cigarette are excessive.